Cargo hooks for aircraft, such as helicopters, must be dependable in operation, of relatively concise size and low weight, capable of being operated by relatively low releasing forces even while carrying loads in excess of 10,000 pounds, and although utilizing engaging abutments and wear surfaces upon which the load is imposed, such surfaces must not unduly become worn or misshapen even though high unit pressures may be imposed thereon during cargo release.
A self-resetting aircraft cargo hook meeting the aforementioned prerequisites and operating characteristics is shown in the assignee's U.S. Pat. No. 3,926,467. The aircraft cargo hook therein described utilizes a plurality of pivotally mounted levers and latches to control the position of a load bearing arm, and by employing a pivotally mounted latch positioned by a cam slot and cam follower arrangement, and utilizing a roller for engaging a latch arm, the force necessary to release the load is minimized, yet dependable operation is achieved in a concise configuration.
However, with the assignee's aircraft cargo hook structure shown in U.S. Pat. No. 3,926,467 the engagement of various interrelated components permits impact forces to be transmitted therebetween, and the position of various components may be inadvertently altered upon an exterior impact force being applied to the cargo hook structure, which, under extreme conditions, may permit inadvertent release of suspended cargo.
It is an object of the invention to provide a self-resetting aircraft cargo hook capable of supporting heavy suspended loads wherein the hook components are so positioned under load carrying conditions as to resist the transfer of impact forces between engaged components.
A further object of the invention is to provide a releasable self-resetting aircraft cargo hook having low release forces, yet wherein the locking mechanism for the load bearing arm even though operable by low releasing forces will not be inadvertently actuated by impact forces imposed upon the cargo hook structure and the transfer of impact forces between critical latching components is prevented.
Yet a further object of the invention is to provide a self-resetting aircraft hook utilizing a pivoted latch having low release force operating characteristics and utilizing a cam slot receiving a cam follower mounted on a lock arm lever wherein the relationship between the cam slot and follower is such that impact forces applied to the latch will not be imposed upon the cam follower.
In the practice of the invention the basic components of the aircraft cargo hook are located between a pair of spaced plates which are suspended, by appropriate structure, from the underside of an aircraft. Between the spaced plates a load arm is pivotally mounted having abutments which selectively cooperate with abutments defined on a pivoted latch arm, and the position of the latch arm is regulated by a pivotally mounted latch having a roller selectively engagable with the latch arm for holding the latch arm in the position permitting the latch arm to maintain the load arm in a cargo carrying position. The position of the latch is controlled by a lock arm lever pivotally mounted between the plates and the lock arm lever includes a cam follower received within a cam slot defined within the latch wherein pivoting of the lock arm lever will position the latch relative to the latch arm.
The load arm is counterweighted so that, in a free state, it tends to pivot toward the load carrying position and is "self-resetting". Accordingly, after release of the load, the load arm rebounds from a resilient bumper and pivots to the load carrying position which automatically repositions the latch arm permitting the latch to return to a latch arm restraining position resetting the cargo hook for the next cycle of use.
The cam slot defined in the latch is of such a configuration that its association with the lock arm lever follower permits the follower to pivot the latch when the lock arm lever is pivoted by its actuating mechanism. The follower, when the load arm is in a load carrying position, maintains the latch in such a position that the pivot points and force points on the latch are substantially aligned so that forces imposed on the latch during load carrying may be easily resisted to prevent pivoting of the latch. However, when the lock arm lever is pivoted to release the latch, the forces imposed upon the latch by the latch arm aid in movement of the latch in a releasing direction, and the lock arm lever and latch arm hold the latch in an inoperative position during load release.
A fixed abutment, in the form of a pin, is mounted upon the cargo hook plates and engages the lock arm lever to accurately position the lock arm lever in its normal or load carrying position. This normal position of the lock arm lever locates the cam follower within the latch cam slot in spaced relationship to the ends of the cam slot which prevents impact forces imposed upon the latch from being transferred to the cam follower to cause an inadvertent and undesired pivoting of the lock arm lever in the load releasing direction. Accordingly, the cargo hook in accord with the invention is immune to unintentional release due to impact forces being applied against the cargo hook structure.